Varieties of attention-deficit/hyperactivity disorder-related intra-individual variability

Insight into the relationship between brain/behavioral speed and variability in patients with minimal hepatic encephalopathy

OBJECTIVE

Intra-individual variability (IIV) of response reaction times (RTs) and psychomotor slowing were proposed as markers of brain dysfunction in patients with minimal hepatic encephalopathy (MHE), a subclinical disorder of the central nervous system frequently detectable in patients with liver cirrhosis. However, behavioral measures alone do not enable investigations into the neural correlates of these phenomena. The aim of this study was to investigate the electrophysiological correlates of psychomotor slowing and increased IIV of RTs in patients with MHE.

METHODS

Event-related potentials (ERPs), evoked by a stimulus-response (S-R) conflict task, were recorded from a sample of patients with liver cirrhosis, with and without MHE, and a group of healthy controls. A recently presented Bayesian approach was used to estimate single-trial P300 parameters.

RESULTS

Patients with MHE, with both psychomotor slowing and higher IIV of RTs, showed higher P300 latency jittering and lower single-trial P300 amplitude compared to healthy controls. In healthy controls, distribution analysis revealed that single-trial P300 latency increased and amplitude decreased as RTs became longer; however, in patients with MHE the linkage between P300 and RTs was weaker or even absent.

CONCLUSIONS

These findings suggest that in patients with MHE, the loss of the relationship between P300 parameters and RTs is related to both higher IIV of RTs and psychomotor slowing.

SIGNIFICANCE

This study highlights the utility of investigating the relationship between single-trial ERPs parameters along with RT distributions to explore brain functioning in normal or pathological conditions.

[Neurobiology of autism and attention deficit hyperactivity disorder by means of neuroimaging techniques: convergences and divergences]

In the clinical area, some symptoms of attention deficit hyperactivity disorder (ADHD) also present in patients with autism spectrum disorders (ASD). Research has shown that there are alterations in brain circuits that have an impact upon specific cognitive and behavioural failures in each of these disorders. Yet, little research has been conducted on the brain correlates underlying both the similarities and the differences in the symptoms. In this review, the structural and functional meta-analytical studies that have been carried out to date on ADHD and ASD have been analysed. On the one hand, there are convergences in the attentional dorsal, executive functions, visual, somatomotor circuits and the default activation circuit. These similarities can account for the comorbid manifestations between the disorders, such as failure in the integration of information, fine motor control and specific attention processes. On the other hand, specifically in ADHD, there is a deficit in the reward circuit and in the attentional ventral, which are systems involved in the measurement of the effects of reinforcement and monitoring of attention. In ASD, the circuits that are most strongly affected are those involved in social cognition and language processes. In conclusion, there are neuronal correlates in both disorders that explain both the convergent and divergent clinical and behavioural manifestations.

Time-on-task in children with ADHD: an ex-Gaussian analysis

Although it is widely known that high intra-individual variability (IIV) is a key characteristic of attention deficit/hyperactivity disorder (ADHD), a detailed exploration of the IIV pattern during the time course of a cognitive task has never been carried out. In this study, 30 children with ADHD and 30 controls, were administered the Conners' Continuous Performance Task (CPT-II). The across-block individual performance of the groups was analyzed using an ex-Gaussian approach, which enabled a clearer understanding of how individual response times (RTs) fluctuate during a task in comparison with conventional measures of central tendency. While the conventional measures showed a significant group effect on mean RTs but similar RT trends across blocks between the two groups, the ex-Gaussian results revealed no actual differences between the two groups in the normally distributed component of mean RTs (mu). In contrast to the control group, the children with ADHD showed a steep increase in the exponentially distributed component of RTs (tau) across blocks, thereby indicating that extremely long RTs progressively increased soon after the beginning of the task. Taken together, the results demonstrated that sustained attention deficit in ADHD can be detected by analyzing the IIV in the first few task blocks.

Perspective: causes and functional significance of temporal variations in attention control

Attention control describes the human ability to selectively modulate the plethora of sensory signals and internal thoughts. The neural systems of attention control have been studied extensively, warranted by the importance of this ability to daily functioning. Here, we consider an emerging theme in the study of attention control-slow temporal fluctuations. We posit that these fluctuations are functionally significant, and may reflect underlying interactions between the neural systems related to attention control. We explore thought experiments to generate different perspectives on landscapes created by the interactions between attention control networks and the sources of input to these control systems. We examine interactions of the fronto-parietal and the default mode networks in the context of internal cognition, and the noradrenergic modulatory projections in the context of arousal, and we consider the implications of these inter-network dynamics on attention states and attention disorders. Through these thought experiments we highlight the breadth of potential knowledge to be gained from the study of slow fluctuations in attention control.

Integrating impairments in reaction time and executive function using a diffusion model framework

Using Ratcliff's diffusion model and ex-Gaussian decomposition, we directly evaluate the role individual differences in reaction time (RT) distribution components play in the prediction of inhibitory control and working memory (WM) capacity in children with and without ADHD. Children with (n = 91, [Formula: see text] age = 10.2 years, 67 % male) and without ADHD (n = 62, [Formula: see text] age = 10.6 years, 46 % male) completed four tasks of WM and a stop signal reaction time (SSRT) task. Children with ADHD had smaller WM capacities and less efficient inhibitory control. Diffusion model analyses revealed that children with ADHD had slower drift rates (v) and faster non-decision times (Ter), but there were no group differences in boundary separations (a). Similarly, using an ex-Gaussian approach, children with ADHD had larger τ values than non-ADHD controls, but did not differ in μ or σ distribution components. Drift rate mediated the association between ADHD status and performance on both inhibitory control and WM capacity. τ also mediated the ADHD-executive function impairment associations; however, models were a poorer fit to the data. Impaired performance on RT and executive functioning tasks has long been associated with childhood ADHD. Both are believed to be important cognitive mechanisms to the disorder. We demonstrate here that drift rate, or the speed at which information accumulates towards a decision, is able to explain both.

The impact of financial reward contingencies on cognitive function profiles in adult ADHD

Objectives

Although it is well established that cognitive performance in children with attention-deficit/hyperactivity disorder (ADHD) is affected by reward and that key deficits associated with the disorder may thereby be attenuated or even compensated, this phenomenon in adults with ADHD has thus far not been addressed. Therefore, the aim of the present study was to examine the motivating effect of financial reward on task performance in adults with ADHD by focusing on the domains of executive functioning, attention, time perception, and delay aversion.

Methods

We examined male and female adults aged 18–40 years with ADHD (n = 38) along with a matched control group (n = 40) using six well-established experimental paradigms.

Results

Impaired performance in the ADHD group was observed for stop-signal omission errors, n-back accuracy, reaction time variability in the continuous performance task, and time reproduction accuracy, and reward normalized time reproduction accuracy. Furthermore, when rewarded, subjects with ADHD exhibited longer reaction times and fewer false positives in the continuous performance task, which suggests the use of strategies to prevent impulsivity errors.

Conclusions

Taken together, our results support the existence of both cognitive and motivational mechanisms for the disorder, which is in line with current models of ADHD. Furthermore, our data suggest cognitive strategies of “stopping and thinking” as a possible underlying mechanism for task improvement that seems to be mediated by reward, which highlights the importance of the interaction between motivation and cognition in adult ADHD.

Multiple deficits in ADHD: executive dysfunction, delay aversion, reaction time variability, and emotional deficits

BACKGROUND

The notion that ADHD constitutes a heterogeneous disorder is well accepted. However, this study contributes with new important knowledge by examining independent effects of a large range of neuropsychological deficits. In addition, the study investigated whether deficits in emotional functioning constitute a dissociable component of ADHD.

METHOD

The study included children with ADHD (n = 102; 7-13 years) and a control sample individually matched with regard to age and gender. The administered tasks were designed to tap into three different neuropsychological domains: executive functions (i.e., working memory, inhibition, and shifting), delay aversion, and reaction time variability. Parent ratings of emotion regulation and a test of emotion recognition were also included.

RESULTS

Children with ADHD differed significantly from controls on all measures, except for delay aversion and recognition of disgust. No main effects of gender or interaction effects of gender and group were found. More importantly, executive functioning, reaction time variability, and emotional functioning all contributed independently to distinguishing between children with ADHD and controls.

CONCLUSIONS

 The current study supports the view of ADHD as a heterogeneous disorder related to multiple neuropsychological deficits. In addition, emotional functioning appears to be an area of importance for ADHD that needs to be incorporated into future theoretical models.

Decomposing attention-deficit/hyperactivity disorder (ADHD)-related effects in response speed and variability

OBJECTIVE

Slow and variable reaction times (RTs) on fast tasks are such a prominent feature of attention-deficit/hyperactivity disorder (ADHD) that any theory must account for them. However, this has proven difficult because the cognitive mechanisms responsible for this effect remain unexplained. Although speed and variability are typically correlated, it is unclear whether single or multiple mechanisms are responsible for group differences in each. RTs are a result of several semi-independent processes, including stimulus encoding, rate of information processing, speed-accuracy trade-offs, and motor response, which have not been previously well characterized.

METHOD

A diffusion model was applied to RTs from a forced-choice RT paradigm in two large, independent case-control samples (NCohort 1 = 214 and NCohort 2 = 172). The decomposition measured three validated parameters that account for the full RT distribution and assessed reproducibility of ADHD effects.

RESULTS

In both samples, group differences in traditional RT variables were explained by slow information processing speed, and unrelated to speed-accuracy trade-offs or nondecisional processes (e.g., encoding, motor response).

CONCLUSIONS

RT speed and variability in ADHD may be explained by a single information processing parameter, potentially simplifying explanations that assume different mechanisms are required to account for group differences in the mean and variability of RTs.

Is reaction time variability in ADHD mainly at low frequencies?

BACKGROUND

Intraindividual variability in reaction times (RT variability) has garnered increasing interest as an indicator of cognitive and neurobiological dysfunction in children with attention deficit hyperactivity disorder (ADHD). Recent theory and research has emphasized specific low-frequency patterns of RT variability. However, whether group differences are specific to low frequencies is not well examined.

METHOD

Two studies are presented. The first is a quantitative review of seven previously published studies that have examined patterns of RT variability in ADHD. The second provides new data from a substantially larger sample of children than in prior studies (N(Control) = 42; NADHD = 123). The children completed a choice RT task as part of a traditional go/stop task. Fast-Fourier transform analyses were applied to assess patterns of variability.

RESULTS

Quantitative review of previous studies indicated that children with ADHD demonstrate more low-frequency variability than non-ADHD controls (Hedge's g = .39; 95% CI: .16-.62), but an equivalent excess variability in a faster frequency comparison band (g = .36; 95% CI: .03-.69), with a trivial and nonsignificant difference between ESs in each band. New data replicated results of the quantitative review with nearly identical effects in the low-frequency (g = .39; 95% CI: .05-.75) and faster frequency comparison bands (g = .40; 95% CI: .04-.74) and no evidence of diagnosis × frequency interaction (p = .954).

CONCLUSIONS

Results suggest that theories of RT variability in ADHD that focus on low-frequency variability will need to be modified to account for the presence of variability at a broader range of frequencies.

Stimulant side effects and inverted-U: implications for ADHD guidelines

OBJECTIVE

To review literature relevant to a possible prediction of stimulant side effects in attention deficit hyperactivity disorder (ADHD), with implications for guidelines.

METHOD

Recent literature on inverted-U effects of dopamine in the prefrontal cortex (PFC), default mode processing, and motor circuits relevant to stimulant side effects is reviewed.

RESULTS

The literature on inverted-U effects in the PFC suggests that catechol-O-methyltransferase (COMT) Met versus Val polymorphisms may predict excess dopaminergic effects, including headache and introversion in Met/Met subjects, but therapeutic effects in Val/Val subjects, while dopamine transporter polymorphisms may predict motor side effects. In particular, an understanding of 'inverted-U' effects helps to explain why some children may experience side effects while others show improvements at similar dose ranges.

CONCLUSION

Genetic prediction of stimulant side effects should be investigated, particularly given recent controversies in relation to National Health and Medical Research Council guidelines for stimulant use. A better understanding of treatment-emergent effects will also provide a better understanding of therapeutic effects.

A behavioral neuroenergetics theory of ADHD

Energetic insufficiency in neurons due to inadequate lactate supply is implicated in several neuropathologies, including attention-deficit/hyperactivity disorder (ADHD). By formalizing the mechanism and implications of such constraints on function, the behavioral Neuroenergetics Theory (NeT) predicts the results of many neuropsychological tasks involving individuals with ADHD and kindred dysfunctions, and entails many novel predictions. The associated diffusion model predicts that response times will follow a mixture of Wald distributions from the attentive state, and ex-Wald distributions after attentional lapses. It is inferred from the model that ADHD participants can bring only 75-85% of the neurocognitive energy to bear on tasks, and allocate only about 85% of the cognitive resources of comparison groups. Parameters derived from the model in specific tasks predict performance in other tasks, and in clinical conditions often associated with ADHD. The primary action of therapeutic stimulants is to increase norepinephrine in active regions of the brain. This activates glial adrenoceptors, increasing the release of lactate from astrocytes to fuel depleted neurons. The theory is aligned with other approaches and integrated with more general theories of ADHD. Therapeutic implications are explored.

Preliminary evidence for reduced posterror reaction time slowing in hyperactive/inattentive preschool children

BACKGROUND

Attention deficit/hyperactivity disorder (ADHD) has been associated with deficits in self-regulatory cognitive processes, some of which are thought to lie at the heart of the disorder. Slowing of reaction times (RTs) for correct responses following errors made during decision tasks has been interpreted as an indication of intact self-regulatory functioning and has been shown to be attenuated in school-aged children with ADHD. This study attempted to examine whether ADHD symptoms are associated with an early-emerging deficit in posterror slowing.

METHOD

A computerized two-choice RT task was administered to an ethnically diverse sample of preschool-aged children classified as either "control" (n = 120) or "hyperactive/inattentive" (HI; n = 148) using parent- and teacher-rated ADHD symptoms. Analyses were conducted to determine whether HI preschoolers exhibit a deficit in this self-regulatory ability.

RESULTS

HI children exhibited reduced posterror slowing relative to controls on the trials selected for analysis. Supplementary analyses indicated that this may have been due to a reduced proportion of trials following errors on which HI children slowed rather than due to a reduction in the absolute magnitude of slowing on all trials following errors.

CONCLUSIONS

High levels of ADHD symptoms in preschoolers may be associated with a deficit in error processing as indicated by posterror slowing. The results of supplementary analyses suggest that this deficit is perhaps more a result of failures to perceive errors than of difficulties with executive control.

Distinct neural signatures detected for ADHD subtypes after controlling for micro-movements in resting state functional connectivity MRI data

In recent years, there has been growing enthusiasm that functional magnetic resonance imaging (MRI) could achieve clinical utility for a broad range of neuropsychiatric disorders. However, several barriers remain. For example, the acquisition of large-scale datasets capable of clarifying the marked heterogeneity that exists in psychiatric illnesses will need to be realized. In addition, there continues to be a need for the development of image processing and analysis methods capable of separating signal from artifact. As a prototypical hyperkinetic disorder, and movement-related artifact being a significant confound in functional imaging studies, ADHD offers a unique challenge. As part of the ADHD-200 Global Competition and this special edition of Frontiers, the ADHD-200 Consortium demonstrates the utility of an aggregate dataset pooled across five institutions in addressing these challenges. The work aimed to (1) examine the impact of emerging techniques for controlling for “micro-movements,” and (2) provide novel insights into the neural correlates of ADHD subtypes. Using support vector machine (SVM)-based multivariate pattern analysis (MVPA) we show that functional connectivity patterns in individuals are capable of differentiating the two most prominent ADHD subtypes. The application of graph-theory revealed that the Combined (ADHD-C) and Inattentive (ADHD-I) subtypes demonstrated some overlapping (particularly sensorimotor systems), but unique patterns of atypical connectivity. For ADHD-C, atypical connectivity was prominent in midline default network components, as well as insular cortex; in contrast, the ADHD-I group exhibited atypical patterns within the dlPFC regions and cerebellum. Systematic motion-related artifact was noted, and highlighted the need for stringent motion correction. Findings reported were robust to the specific motion correction strategy employed. These data suggest that resting-state functional connectivity MRI (rs-fcMRI) data can be used to characterize individual patients with ADHD and to identify neural distinctions underlying the clinical heterogeneity of ADHD.

Cognitive variability in adults with ADHD and AS: disentangling the roles of executive functions and social cognition

Attention-deficit/hyperactivity disorder (ADHD) and Asperger's Syndrome (AS) share a heterogeneous cognitive profile. Studies assessing executive functions (EF) and social cognition in both groups have found preserved and impaired performances. These inconsistent findings would be partially explained by the cognitive variability reported in these disorders. First, the present study explored the inter-individual variability in EF and social cognition in both patient groups. Second, we compared differential characteristics and commonalities in the cognitive profiles of EF and social cognition between ADHD, AS and control adults. We assessed 22 patients with ADHD, 23 adults with AS and 21 matched typically developing subjects using different measures of EF (working memory, cognitive flexibility and multitasking) and social cognition (theory of mind and decision-making). Group comparisons and multiple case series analyses (MCSA) were conducted. The between-group comparisons showed an EF deficit in working memory in ADHD and a theory of mind (ToM) impairment in AS. The MCSA evidenced that, compared to controls, ADHD patients had a higher inter-individual variability in EF, while individuals with AS had a more heterogeneous profile in social cognition tasks compared to both groups. Finally, the AS and ADHD groups presented higher task-related variability compared to controls and shared a common heterogeneous profile in EF. This is the first study to compare variability in EF and social cognition profiles of ADHD and AS. We propose that heterogeneity in EF performance is a link between ADHD and AS which may explain the overlap of symptomatology between both diagnoses. In addition, patients with AS seem to show a unique heterogeneous profile in ToM which may explain the low probability of finding AS symptoms in patients with ADHD.

Reaction time variability in children with ADHD symptoms and/or dyslexia

Reaction time (RT) variability on a Stop Signal task was examined among children with attention deficit hyperactivity disorder (ADHD) symptoms and/or dyslexia in comparison to typically developing (TD) controls. Children's go-trial RTs were analyzed using a novel ex-Gaussian method. Children with ADHD symptoms had increased variability in the fast but not the slow portions of their RT distributions compared to those without ADHD symptoms. The RT distributions of children with dyslexia were similar to those of TD-controls. It is argued that variability in responding may be underpinned by impairments in response preparation or timing during Stop Signal tasks.

Low-frequency fluctuation in continuous real-time feedback of finger force: a new paradigm for sustained attention

OBJECTIVE

Behavioral studies have suggested a low-frequency (0.05 Hz) fluctuation of sustained attention on the basis of the intra-individual variability of reaction-time. Conventional task designs for functional magnetic resonance imaging (fMRI) studies are not appropriate for frequency analysis. The present study aimed to propose a new paradigm, real-time finger force feedback (RT-FFF), to study the brain mechanisms of sustained attention and neurofeedback.

METHODS

We compared the low-frequency fluctuations in both behavioral and fMRI data from 38 healthy adults (19 males; mean age, 22.3 years). Two fMRI sessions, in RT-FFF and sham finger force feedback (S-FFF) states, were acquired (TR 2 s, Siemens Trio 3-Tesla scanner, 8 min each, counter-balanced). Behavioral data of finger force were obtained simultaneously at a sampling rate of 250 Hz.

RESULTS

Frequency analysis of the behavioral data showed lower amplitude in the low-frequency band (0.004-0.104 Hz) but higher amplitude in the high-frequency band (27.02-125 Hz) in the RT-FFF than the S-FFF states. The mean finger force was not significantly different between the two states. fMRI data analysis showed higher fractional amplitude of low-frequency fluctuation (fALFF) in the S-FFF than in the RT-FFF state in the visual cortex, but higher fALFF in RT-FFF than S-FFF in the middle frontal gyrus, the superior frontal gyrus, and the default mode network.

CONCLUSION

The behavioral results suggest that the proposed paradigm may provide a new approach to studies of sustained attention. The fMRI results suggest that a distributed network including visual, motor, attentional, and default mode networks may be involved in sustained attention and/or real-time feedback. This paradigm may be helpful for future studies on deficits of attention, such as attention deficit hyperactivity disorder and mild traumatic brain injury.

Unreliable evoked responses in autism

Autism has been described as a disorder of general neural processing, but the particular processing characteristics that might be abnormal in autism have mostly remained obscure. Here, we present evidence of one such characteristic: poor evoked response reliability. We compared cortical response amplitude and reliability (consistency across trials) in visual, auditory, and somatosensory cortices of high-functioning individuals with autism and controls. Mean response amplitudes were statistically indistinguishable across groups, yet trial-by-trial response reliability was significantly weaker in autism, yielding smaller signal-to-noise ratios in all sensory systems. Response reliability differences were evident only in evoked cortical responses and not in ongoing resting-state activity. These findings reveal that abnormally unreliable cortical responses, even to elementary nonsocial sensory stimuli, may represent a fundamental physiological alteration of neural processing in autism. The results motivate a critical expansion of autism research to determine whether (and how) basic neural processing properties such as reliability, plasticity, and adaptation/habituation are altered in autism.

Neuropsychological performance and attention-deficit hyperactivity disorder subtypes and symptom dimensions

OBJECTIVE

Characterization of clinical heterogeneity in attention-deficit hyperactivity disorder (ADHD) remains controversial. Neuropsychological and cognitive studies provide one type of validation data, but too often have considered only a narrow range of functional domains.

METHOD

The current study examined ADHD subtype and presentation differences across a broad range of neurocognitive domains in a large clinically characterized, community-recruited sample of 498 youth (213 control, 107 ADHD-primarily inattentive [ADHD-PI], 137 ADHD-combined [ADHD-C]), ages 6-17 years. Domains assessed included inhibition, working memory, arousal, processing speed, response variability, and temporal information processing.

RESULTS

Youth with ADHD-C performed worse than youth with ADHD-PI in all domains, consistent with a severity model. Performance among a subgroup with a "restrictive inattentive" presentation indicated potential deficits in processing speed relative to other ADHD-PI youth, but no other effects. When all measures were included in the same model, cognitive control (executive functions, working memory, and memory span), arousal, and response variability each provided uniquely incremental statistical prediction of specific symptom dimensions and of subtype/presentation, but temporal information processing and processing speed did not.

CONCLUSION

Results suggest the potential to consolidate multiple neurocognitive theories of ADHD, and that such consolidation will apply across putative clinical subtypes or presentations.

Effects of methylphenidate on basic and higher-order oculomotor functions

Eye movements are sensitive indicators of pharmacological effects on sensorimotor and cognitive processing. Methylphenidate (MPH) is one of the most prescribed medications in psychiatry. It is increasingly used as a cognitive enhancer by healthy individuals. However, little is known of its effect on healthy cognition. Here we used oculomotor tests to evaluate the effects of MPH on basic oculomotor and executive functions. Twenty-nine males were given 20mg of MPH orally in a double-blind placebo-controlled crossover design. Participants performed visually-guided saccades, sinusoidal smooth pursuit, predictive saccades and antisaccades one hour post-capsule administration. Heart rate and blood pressure were assessed prior to capsule administration, and again before and after task performance. Visually-guided saccade latency decreased with MPH (p<0.004). Smooth pursuit gain increased on MPH (p<0.001) and number of saccades during pursuit decreased (p<0.001). Proportion of predictive saccades increased on MPH (p<0.004), specifically in conditions with predictable timing. Peak velocity of predictive saccades increased with MPH (p<0.01). Antisaccade errors and latency were unaffected. Physiological variables were also unaffected. The effects on visually-guided saccade latency and peak velocity are consistent with MPH effects on dopamine in basal ganglia. The improvements in predictive saccade conditions and smooth pursuit suggest effects on timing functions.

Does atomoxetine improve executive function, inhibitory control, and hyperactivity? Results from a placebo-controlled trial using quantitative measurement technology

The primary objective of this study was to evaluate the efficacy of atomoxetine (ATX) on attention-deficit/hyperactivity disorder (ADHD)-related symptoms assessed as standard variables of a computer-based continuous performance test (cb-CPT) combined with a motion-tracking (MT) device. This was a 2-arm, 8-week, randomized, double-blind, placebo-controlled study in patients with ADHD (6-12 years). Therapy with ATX started with 0.5 mg/kg per day for 1 week, followed by 7 weeks on the target dosage of 1.2 mg/kg per day. Primary outcomes were cb-CPT/MT standard scores after 8 weeks using mixed models for repeated measurements. In addition, investigator-rated ADHD Rating Scale (ADHD-RS), Weekly Ratings of Evening and Morning Behavior (WREMB), and Clinical Global Impression - Severity-ADHD (CGI-S-ADHD) scores were assessed. Of 128 patients randomized, 125 were evaluated (ATX/placebo: 63/62). Baseline characteristics were comparable in both groups (overall, 80.2% boys; mean [SD] age, 9.0 [1.79] years; comorbid Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition diagnosis, 40.0% oppositional defiant disorder/conduct disorder; prior stimulant treatment, 24.8%; ADHD-RS total score, 36.99 [11.56]). At week 8, all cb-CPT/MT q-scores were significantly reduced versus placebo (all P < 0.001) with effect sizes (ESs) of reaction time (RT) variation (ES = 0.71), mean RT (ES = 0.41), number of microevents (ES = 1.00), commission error rate (ES = 0.50), distance of movement (ES = 0.90), area of movement (ES = 1.08), omission error rate (ES = 0.70), time active (ES = 0.69), motion simplicity (ES = 0.38), and normalized variance of RT (ES = 0.50). Secondary end points also improved significantly in favor of ATX: ADHD-RS (total score ES = 1.30, P < 0.001; hyperactivity/impulsivity subscore ES = 1.37, P < 0.001; inattention subscore ES = 1.07, P < 0.001), WREMB (total score ES = 1.00, P < 0.001; morning subscore ES = 0.59, P = 0.002; evening subscore ES = 1.02, P < 0.001), CGI-S-ADHD (ES = 1.11, P < 0.001). The results of this study show that ATX for 8 weeks significantly reduced ADHD-related symptoms as measured by the cb-CPT/MT.

Abnormal brain connectivity patterns in adults with ADHD: a coherence study

Studies based on functional magnetic resonance imaging (fMRI) during the resting state have shown decreased functional connectivity between the dorsal anterior cingulate cortex (dACC) and regions of the Default Mode Network (DMN) in adult patients with Attention-Deficit/Hyperactivity Disorder (ADHD) relative to subjects with typical development (TD). Most studies used Pearson correlation coefficients among the BOLD signals from different brain regions to quantify functional connectivity. Since the Pearson correlation analysis only provides a limited description of functional connectivity, we investigated functional connectivity between the dACC and the posterior cingulate cortex (PCC) in three groups (adult patients with ADHD, n = 21; TD age-matched subjects, n = 21; young TD subjects, n = 21) using a more comprehensive analytical approach – unsupervised machine learning using a one-class support vector machine (OC-SVM) that quantifies an abnormality index for each individual. The median abnormality index for patients with ADHD was greater than for TD age-matched subjects (p = 0.014); the ADHD and young TD indices did not differ significantly (p = 0.480); the median abnormality index of young TD was greater than that of TD age-matched subjects (p = 0.016). Low frequencies below 0.05 Hz and around 0.20 Hz were the most relevant for discriminating between ADHD patients and TD age-matched controls and between the older and younger TD subjects. In addition, we validated our approach using the fMRI data of children publicly released by the ADHD-200 Competition, obtaining similar results. Our findings suggest that the abnormal coherence patterns observed in patients with ADHD in this study resemble the patterns observed in young typically developing subjects, which reinforces the hypothesis that ADHD is associated with brain maturation deficits.

Reaction time variability in ADHD: a review

For the past decade, intra-individual variability in reaction times on computerized tasks has become a central focus of cognitive research on Attention-Deficit/Hyperactivity Disorder (ADHD). Numerous studies document increased reaction time variability among children and adults with ADHD, relative to typically developing controls. However, direct comparisons with other disorders with heightened reaction time variability are virtually nonexistent, despite their potential to inform our understanding of the phenomenon. A growing literature examines the sensitivity of reaction time variability to theoretically and clinically relevant manipulations. There is strong evidence that stimulus treatment reduces reaction time variability during a range of cognitive tasks, but the literature is mixed regarding the impact of motivational incentives and variation in stimulus event rate. Most studies of reaction time variability implicitly assume that heightened reaction time variability reflects occasional lapses in attention, and the dominant neurophysiological interpretation suggests this variability is linked to intrusions of task-negative brain network activity during task performance. Work examining the behavioral and neurophysiological correlates of reaction time variability provides some support for these hypotheses, but considerably more work is needed in this area. Finally, because conclusions from each of domains reviewed are limited by the wide range of measures used to measure reaction time variability, this review highlights the need for increased attention to the cognitive and motivational context in which variability is assessed and recommends that future work always supplement macro-level variability indices with metrics that isolate particular components of reaction time variability.

Sex modifies genetic effects on residual variance in urinary calcium excretion in rat (Rattus norvegicus)

Conventional genetics assumes common variance among alleles or genetic groups. However, evidence from vertebrate and invertebrate models suggests that residual genotypic variance may itself be under partial genetic control. Such a phenomenon would have great significance: high-variability alleles might confound the detection of "classically" acting genes or scatter predicted evolutionary outcomes among unpredicted trajectories. Of the few works on this phenomenon, many implicate sex in some aspect of its control. We found that female genetic hypercalciuric stone-forming (GHS) rats (Rattus norvegicus) had higher coefficients of variation (CVs) for urinary calcium (CV = 0.14) than GHS males (CV = 0.06), and the reverse in normocalciuric Wistar-Kyoto rats (WKY) (CV(♂) = 0.14; CV(♀) = 0.09), suggesting sex-by-genotype interaction on residual variance. We therefore investigated the effect of sex on absolute-transformed residuals in urinary calcium in an F(2) GHS × WKY mapping cohort. Absolute residuals were associated with genotype at two microsatellites, D3Rat46 (RNO3, 33.9 Mb) and D4Mgh1 (RNO4, 84.8 MB) at Bonferroni thresholds across the entire cohort, and with the microsatellites D3Rat46, D9Mgh2 (RNO9, 84.4 Mb), and D12Rat25 (RNO12, 40.4 Mb) in females (P < 0.05) but not males. In GHS chromosome 1 congenic lines bred onto a WKY genomic background, we found that congenic males had significantly (P < 0.0001) higher CVs for urinary calcium (CV = 0.25) than females (CV = 0.15), supporting the hypothesis of the inheritance of sex-by-genotype interaction on this effect. Our findings suggest that genetic effects on residual variance are sex linked; heritable, sex-specific residuals might have great potential implications for evolution, adaptation, and genetic analysis.

Shared genetic influences on ADHD symptoms and very low-frequency EEG activity: a twin study

BACKGROUND

  Attention deficit hyperactivity disorder (ADHD) is a common and highly heritable neurodevelopmental disorder with a complex aetiology. The identification of candidate intermediate phenotypes that are both heritable and genetically linked to ADHD may facilitate the detection of susceptibility genes and elucidate aetiological pathways. Very low-frequency (VLF; <0.5 Hz) electroencephalographic (EEG) activity represents a promising indicator of risk for ADHD, but it currently remains unclear as to whether it is heritable or genetically linked to the disorder.

METHODS

  Direct-current (DC)-EEG was recorded during a cognitive activation condition in 30 monozygotic and dizygotic adolescent twin pairs concordant or discordant for high ADHD symptom scores, and 37 monozygotic and dizygotic matched-control twin pairs with low ADHD symptom scores. Structural equation modelling was used to quantify the genetic and environmental contributions to the phenotypic covariance between ADHD and VLF activity.

RESULTS

  Attention deficit hyperactivity disorder was significantly associated with reduced VLF power during cognitive activation, which suggests reduced synchronization of widespread neuronal activity. Very low-frequency power demonstrated modest heritability (0.31), and the genetic correlation (-0.80) indicated a substantial degree of overlap in genetic influences on ADHD and VLF activity.

CONCLUSIONS

  Altered VLF activity is a potential candidate intermediate phenotype of ADHD, which warrants further investigation of underlying neurobiological and genetic mechanisms.

The default mode network and recurrent depression: a neurobiological model of cognitive risk factors

A neurobiological account of cognitive vulnerability for recurrent depression is presented based on recent developments of resting state neural networks. We propose that alterations in the interplay between task positive (TP) and task negative (TN) elements of the Default Mode Network (DMN) act as a neurobiological risk factor for recurrent depression mediated by cognitive mechanisms. In the framework, depression is characterized by an imbalance between TN-TP components leading to an overpowering of TP by TN activity. The TN-TP imbalance is associated with a dysfunctional internally-focused cognitive style as well as a failure to attenuate TN activity in the transition from rest to task. Thus we propose the TN-TP imbalance as overarching neural mechanism involved in crucial cognitive risk factors for recurrent depression, namely rumination, impaired attentional control, and cognitive reactivity. During remission the TN-TP imbalance persists predisposing to vulnerability of recurrent depression. Empirical data to support this model is reviewed. Finally, we specify how this framework can guide future research efforts.

Cognitive functioning and family risk factors in relation to symptom behaviors of ADHD and ODD in adolescents

OBJECTIVE

In this study, the authors investigated whether ADHD and oppositional defiant disorder (ODD) behaviors share associations with problems in cognitive functioning and/or family risk factors in adolescence. This was done by examining independent as well as specific associations of cognitive functioning and family risk factors with ADHD and ODD behaviors.

METHOD

A sample of 120 adolescents from the general population was assessed on various cognitive tasks. ADHD and ODD behaviors were measured through parental and teacher ratings based on Diagnostic and Statistical Manual of Mental Disorders (4th edition) criteria. Parents and adolescents provided information regarding measures of family risk factors.

RESULTS

The results show that only cognitive functioning was associated with ADHD behaviors, and family risk factors were, independent of cognitive functioning, associated with ODD behaviors.

CONCLUSION

These results suggest that cognitive performance bears a specific significance for ADHD behaviors, whereas family risk factors have specific importance for ODD behaviors.

Differential effects of methylphenidate and atomoxetine on attentional processes in children with ADHD: an event-related potential study using the Attention Network Test

Methylphenidate (MPH) and atomoxetine (ATX) are effective medications in the treatment of attention deficit/hyperactivity disorder (ADHD). The aim of this study was to investigate differential effects of MPH and ATX on attentional functions at the performance and the neuronal level in children with ADHD. Using the Attention Network Test (ANT), differential effects of both medications on the noradrenergic alerting network and the dopaminergic executive attention network were considered. Nineteen children with ADHD performed the ANT three times while event-related potentials (ERPs) were recorded. The baseline testing was conducted without medication. In two medication blocks of 8 weeks each, medication was individually titrated for each child (cross-over design, balanced order). At the end of the medication blocks the testing was repeated. While both medications comparably reduced ADHD symptomatology, MPH had some advantages over ATX with regard to performance measures on the ANT and the underlying neuronal mechanisms. Compared with ATX, MPH led to a larger reduction in reaction time variability, which was accompanied by an MPH-related increase in the contingent negative variation (CNV) compared to the baseline testing. Contrary to our expectations, specific alerting network effects were not observed with ATX. Due to the chosen study design, it remains unresolved to what extent e.g. shortened reaction times and smaller conflict scores that were observed with both medications reflect practice or medication effects. The differential pattern of MPH vs. ATX effects on attentional functions in children with ADHD may be explained by the dopaminergic effects of MPH within the cortico-striato-thalamo-cortical circuit.

Modulation of attention-deficit/hyperactivity disorder symptoms by short- and long-acting methylphenidate over the course of a day

The purpose of this study was to investigate whether a long-acting methylphenidate formulation (MPH-ret) is as effective as two doses of immediate-release methylphenidate (MPH-IR) in reducing attention-deficit/hyperactivity disorder (ADHD) symptoms including inattention, impulsivity, and hyperactivity during the course of the day. Two groups of children (n=18 each) with ADHD aged between 8 and 12 years completed a continuous performance test in combination with a motion-tracking system four times a day within 8 hours. Inattention (standard deviation of reaction time), impulsivity (commission error rate), and hyperactivity (path length of the headband) were simultaneously measured. We included a control group (n=20) to rule out circadian fluctuations of attentional performance and motor activity. We observed a postlunch dip in attentional performance and an increasing trend of motor activity throughout the day whereas impulsivity remained stable in controls. The MPH-ret and MPH-IR groups had comparable treatment effects on measures of hyperactivity and inattention and normalized participant performance to control levels. In contrast, MPH-IR seems to have an advantage over MPH-ret in impulsivity treatments. Thus, our data suggest that it is crucial to assess the different domains of ADHD symptoms precisely over the course of a day to determine the optimal titration and stimulant formulation for a person with ADHD.

Evaluating vigilance deficits in ADHD: a meta-analysis of CPT performance

We meta-analytically review 47 between-groups studies of continuous performance test (CPT) performance in children with attention-deficit/hyperactivity disorder (ADHD). Using a random effects model and correcting for both sampling error and measurement unreliability, we found large effect sizes (δ) for overall performance, but only small to moderate δ for performance over time in the handful of studies that reported that data. Smaller δs for performance over time are likely attributable, in part, to the extensive use of stimuli for which targets and distractors are quite easily differentiated. Artifacts accounted for a considerable proportion of variance among observed δs. Effect sizes reported in previous reviews were significantly attenuated because of the presence of uncorrected artifacts and highlight the necessity of accounting for artifactual variance in future work to determine the amount of true neurocognitive heterogeneity within ADHD. Signal detection theory and diffusion modeling analyses indicated that the ADHD-related deficits were because of decreased perceptual sensitivity (d') and slower drift rates (v). Results are interpreted the context of several recent models of ADHD.

Dopaminergic polymorphisms associated with time-on-task declines and fatigue in the Psychomotor Vigilance Test

Prolonged demands on the attention system can cause a decay in performance over time known as the time-on-task effect. The inter-subject differences in the rate of this decline are large, and recent efforts have been made to understand the biological bases of these individual differences. In this study, we investigate the genetic correlates of the time-on-task effect, as well as its accompanying changes in subjective fatigue and mood. N = 332 subjects performed a 20-minute test of sustained attention (the Psychomotor Vigilance Test) and rated their subjective states before and after the test. We observed substantial time-on-task effects on average, and large inter-individual differences in the rate of these declines. The 10-repeat allele of the variable number of tandem repeats marker (VNTR) in the dopamine transporter gene and the Met allele of the catechol-o-methyl transferase (COMT) Val158Met polymorphism were associated with greater vulnerability to time-on-task. Separately, the exon III DRD4 48 bp VNTR of the dopamine receptor gene DRD4 was associated with subjective decreases in energy. No polymorphisms were associated with task-induced changes in mood. We posit that the dopamine transporter and COMT genes exert their effects by increasing dopaminergic tone, which may induce long-term changes in the prefrontal cortex, an important mediator of sustained attention. Thus, these alleles may affect performance particularly when sustained dopamine release is necessary.

Behavioural treatment increases activity in the cognitive neuronal networks in children with attention deficit/hyperactivity disorder

Response cost and token approach (RCT) within the scope of a summer camp training is an effective treatment program for attention deficit hyperactivity disorder (ADHD). It is likely that intensive RCT training influences networks responsible for ADHD symptoms. Functional magnetic resonance imaging (fMRI) was carried out in 12 children with ADHD before and after the RCT program and in 12 healthy control children twice. For fMRI, a Go/No-go paradigm was used to investigate the influence of RCT training on attention and impulsivity. The No-go condition revealed only weak activation in the dorsal part of the anterior cingulate cortex (ACC), parietal and dorsolateral prefrontal cortex (DLPFC) before the training in children with ADHD compared to healthy children. However, this activation in these brain regions was significantly more pronounced after the training. This increase in hemodynamic response cannot be attributed merely to repetition of the measurement since the effect was not observed in healthy children. The increase in hemodynamic response in the ACC and right DLPFC was significantly associated with a reduction in response time variability and clinical symptoms in ADHD patients. After the RCT training, the children with ADHD demonstrated more pronounced activation of cortical structures which are typically related to response monitoring and self-control. It seems likely that children with ADHD learned more cognitive control in a continuous performance task as was revealed by both neuropsychological outcome and fMRI.

Neuropsychological intra-individual variability explains unique genetic variance of ADHD and shows suggestive linkage to chromosomes 12, 13, and 17

Attention-deficit/hyperactivity disorder (ADHD) is a highly heritable neuropsychiatric disorder that is usually accompanied by neuropsychological impairments. The use of heritable, psychometrically robust traits that show association with the disorder of interest can increase the power of gene-finding studies. Due to the robust association of intra-individual variability with ADHD on a phenotypic and genetic level, intra-individual variability is a prime candidate for such an attempt. We aimed to combine intra-individual variability measures across tasks into one more heritable measure, to examine the relatedness to other cognitive factors, and to explore the genetic underpinnings through quantitative trait linkage analysis. Intra-individual variability measures from seven tasks were available for 238 ADHD families (350 ADHD-affected and 195 non-affected children) and 147 control families (271 children). Intra-individual variability measures from seven different tasks shared common variance and could be used to construct an aggregated measure. This aggregated measure was largely independent from other cognitive factors related to ADHD and showed suggestive linkage to chromosomes 12q24.3 (LOD = 2.93), 13q22.2 (LOD = 2.36), and 17p13.3 (LOD = 2.00). A common intra-individual variability construct can be extracted from very diverse neuropsychological tasks; this construct taps into unique genetic aspects of ADHD and may relate to loci conferring risk for ADHD (12q24.3 and 17p13.3) and possibly autism (12q24.3). Given that joining of data across sites boosts the power for genetic analyses, our findings are promising in showing that intra-individual variability measures are viable candidates for across site analyses where different tasks have been used.

Dimensional brain-behavior relationships in children with attention-deficit/hyperactivity disorder

BACKGROUND

Emerging neuroscientific and genetic findings emphasize the dimensional rather than the categorical aspects of psychiatric disorders. However, the integration of dimensional approaches within the current categorical diagnostic framework remains unclear. Here, we used resting state functional magnetic resonance imaging to examine whether dimensional measures of psychiatric symptomatology capture brain-behavior relationships unaccounted for by categorical diagnoses. Additionally, we examined whether dimensional brain-behavior relationships are modified by the presence of a categorically defined illness, attention-deficit/hyperactivity disorder (ADHD).

METHODS

Resting state functional magnetic resonance imaging scans were collected from 37 typically developing children (aged 10.2 ± 2; 21 female subjects) and 37 children meeting DSM-IV Text Revision criteria for ADHD (9.7 ± 2; 11 female subjects). Parent-rated Child Behavior Checklist Externalizing and Internalizing scores served as dimensional measures in our analyses of default network (DN) resting state functional connectivity (RSFC).

RESULTS

Regardless of diagnosis, we observed several significant relationships between DN RSFC and both internalizing and externalizing scores. Increased internalizing scores were associated with stronger positive intra-DN RSFC, while increased externalizing scores were associated with reduced negative RSFC between DN and task-positive regions such as dorsal anterior cingulate cortex. Several of these brain-behavior relationships differed depending on the categorical presence of ADHD.

CONCLUSIONS

Our findings suggest that while categorical diagnostic boundaries provide an inadequate basis for understanding the pathophysiology of psychiatric disorders, psychiatric illness cannot be viewed simply as an extreme of typical neural or behavioral function. Efforts to understand the neural underpinnings of psychiatric illness should incorporate both categorical and dimensional clinical assessments.

Increased intra-individual reaction time variability in cocaine-dependent subjects: role of cocaine-related cues

Neuroimaging data suggest that impaired performance on response inhibition and information processing tests in cocaine-dependent subjects is related to prefrontal and frontal cortical dysfunction and that dysfunction in these brain areas may underlie some aspects of cocaine addiction. In subjects with attention-deficit hyperactivity disorder and other psychiatric disorders, the Intra-Individual Reaction Time Variability (IIRTV) has been associated with frontal cortical dysfunction. In the present study, we evaluated IIRTV parameters in cocaine-dependent subjects vs. controls using a cocaine Stroop task. Fifty control and 123 cocaine-dependent subjects compiled from three studies completed a cocaine Stroop task. Standard deviation (SD) and coefficient of variation (CV) for reaction times (RT) were calculated for both trials with neutral and trials with cocaine-related words. The parameters mu, sigma, and tau were calculated using an ex-Gaussian analysis employed to characterize variability in RTs. The ex-Gaussian analysis divides the RTs into normal (mu, sigma) and exponential (tau) components. Using robust regression analysis, cocaine-dependent subjects showed greater SD, CV and Tau on trials with cocaine-related words compared to controls (p<0.05). However, in trials with neutral words, there was no evidence of group differences in any IIRTV parameters (p>0.05). The Wilcoxon matched-pairs signed-rank test showed that for cocaine-dependent subjects, both SD and tau were larger in trials with cocaine-related words than in trials with neutral words (p<0.05). The observation that only cocaine-related words increased IIRTV in cocaine-dependent subjects suggests that cocaine-related stimuli might disrupt information processing subserved by prefrontal and frontal cortical circuits.

Low frequency oscillations of response time explain parent ratings of inattention and hyperactivity/impulsivity

Greater intra-subject variability (ISV) in response time is a heritable endophenotype of attention-deficit/hyperactivity disorder (ADHD). Spontaneous low frequency oscillations (LFO: 0.01-0.1 Hz) observed in brain functional magnetic resonance signals might account for such behavioral variability. Recently, we demonstrated that ISV in response time (RT) explained ratings of ADHD symptoms. Building on this finding, here we hypothesized that LFO in RT time series would explain these ratings, both independently and in addition to RT coefficient of variation (CV). To measure RT LFO, we applied Morlet wavelet transform to the previously collected RT data. Our community sample consisted of 98 children (including 66 boys, mean age 9.9 ± 1.4 years), who completed four computer Tasks of Executive Control. Conners' Parent Rating Scale ratings were obtained. RT LFO of three tasks significantly explained ratings of inattention, hyperactivity and three global Conners' subscales. In addition, RT LFO during two tasks that included an inhibitory component increased the proportions of variance explained in subscales of both inattention and hyperactivity/impulsivity, beyond the effects of RT-CV. Three specific low frequency bands (Slow-5: 0.01-0.027 Hz; Slow-4: 0.027-0.073 Hz; Slow-3: 0.073-0.20 Hz) were strongly related to the ADHD scales. We conclude that RT LFO predict dimensional ratings of ADHD symptoms both independently and in addition to RTCV. Results suggest that frequency analyses are a suitable methodology to link behavioral responses to putative underlying physiological processes.

Intra-individual variability among children with ADHD on a working memory task: an ex-Gaussian approach

Intra-individual variability on a computer-based working memory task was examined among 25 children/adolescents with ADHD and 24 typically developing peers. Participants completed the Visual Serial Addition Task (VSAT) and reaction time data were fit to an ex-Gaussian distribution. ADHD participants demonstrated significantly more variable performance than controls, and effects of working memory load were observed. Event rate, however, had no influence on group differences in performance. Follow-up correlations revealed associations between VSAT performance and ADHD symptomatology. This study supports intra-individual variability as a hallmark feature of ADHD beyond the domain of response inhibition and reinforces the need to consider variability in ADHD more broadly.

Interference control in children with and without ADHD: a systematic review of Flanker and Simon task performance

The present review systematically summarizes the existing research that has examined two reaction-time-based interference control paradigms, known as the Eriksen Flanker task and the Simon task, in children with and without ADHD. Twelve studies are included, yielding a combined sample size of 272 children with ADHD (M age 9.28 yrs) and 280 typically developing children (M age 9.38 yrs). As predicted, specific disadvantages were found in the ADHD group in terms of reaction time, percentage of errors, and efficiency of performance on incongruent relative to congruent trials, providing evidence for weaker interference control in this group.

Linking ADHD, impulsivity, and drug abuse: a neuropsychological perspective

In this chapter, we consider the relevance of impulsivity as both a psychological construct and endophenotype underlying attention-deficit/hyperactivity disorder (ADHD) and drug addiction. The case for executive dysfunction in ADHD and drug addiction is critically reviewed in the context of dissociable cognitive control processes mediated by the dorsolateral prefrontal cortex (DLPFC), the orbital and ventral medial prefrontal cortex (VMPFC). We argue that such neuroanatomical divisions within the prefrontal cortex are likely to account for the multidimensional basis of impulsivity conceptually categorized in terms of "motoric" and "choice" impulsivity. The relevance of this distinction for the etiology of ADHD and drug addiction is integrated within a novel theoretical framework. This scheme embraces animal learning theory to help explain the heterogeneity of impulse control disorders, which are exemplified by ADHD as a vulnerability disorder for drug addiction.

Rat models of ADHD

Showing that an animal is hyperactive is not sufficient for it to be accepted as a model of ADHD. Based on behavioral, genetic, and neurobiological data, the spontaneously hypertensive rat (SHR) obtained from Charles River, Germany, (SHR/NCrl) is at present the best-validated animal model of ADHD. One Wistar Kyoto substrain (WKY/NHsd), obtained from Harlan, UK, is its most appropriate control. Another WKY substrain (WKY/NCrl) obtained from Charles River, Germany, is inattentive, has distinctly different genetics and neurobiology, and provides a promising model for the predominantly inattentive subtype of ADHD (ADHD-I) if one wants to investigate categorical ADHD subtypes. In this case, also, the WKY/NHsd substrain should be used as control. Although other rat strains may behave like WKY/NHsd rats, neurobiological results indicate significant differences when compared to the WKY/NHsd substrain, making them less suitable as controls for the SHR/NCrl. Thus, there are no obvious behavioral differences among the various SHRs, but there are behavioral and neurobiological differences among the WKY strains. The use of WKY/NCrl, outbred Wistar, Sprague Dawley, or other rat strains as controls for SHR/NCrl may produce spurious neurobiological effects and erroneous conclusions. Finally, model data yield support to independent hyperactivity and inattention dimensions in ADHD behavior.

Falls and falls efficacy: the role of sustained attention in older adults

BACKGROUND

Previous evidence indicates that older people allocate more of their attentional resources toward their gait and that the attention-related changes that occur during aging increase the risk of falls. The aim of this study was to investigate whether performance and variability in sustained attention is associated with falls and falls efficacy in older adults.

METHODS

458 community-dwelling adults aged ≥ 60 years underwent a comprehensive geriatric assessment. Mean and variability of reaction time (RT), commission errors and omission errors were recorded during a fixed version of the Sustained Attention to Response Task (SART). RT variability was decomposed using the Fast Fourier Transform (FFT) procedure, to help characterise variability associated with the arousal and vigilance aspects of sustained attention.The number of self-reported falls in the previous twelve months, and falls efficacy (Modified Falls Efficacy Scale) were also recorded.

RESULTS

Significant increases in the mean and variability of reaction time on the SART were significantly associated with both falls (p < 0.01) and reduced falls efficacy (p < 0.05) in older adults. An increase in omission errors was also associated with falls (p < 0.01) and reduced falls efficacy (p < 0.05). Upon controlling for age and gender affects, logistic regression modelling revealed that increasing variability associated with the vigilance (top-down) aspect of sustained attention was a retrospective predictor of falling (p < 0.01, OR = 1.14, 95% CI: 1.03-1.26) in the previous year and was weakly correlated with reduced falls efficacy in non-fallers (p = 0.07).

CONCLUSIONS

Greater variability in sustained attention is strongly correlated with retrospective falls and to a lesser degree with reduced falls efficacy. This cognitive measure may provide a novel and valuable biomarker for falls in older adults, potentially allowing for early detection and the implementation of preventative intervention strategies.